If you just look at the 3dmax scores in the benchmarks, linked above, then there is a substantial gain from I7 950 over the 965BE. Whether it is worth the money is a question you will have to answer.
On average the AMD is only 5 seconds or so behind the much more expensive i7-950. That is not really that substantial to replace what he has. That's like buying a new car that can only go 100 mph and wanting to change it for a much higher priced car that can go 110 mph. Unless he maxes the system 24/7, those sheer seconds don't add up to much (surely less than 15 minutes in the whole work day). As for the 2500k, that will wipe the 965 away and offers clear justification to replace the 965. But if you only consider 3D scores alone, there is also not a huge benefit from the 2500k, just 1-2 seconds over the i7-950... but over all system responsiveness and performance is 25% better than both and it is cheaper than the i7-950.